The present invention relates to an improved elevator control system.
In general, the electric power consumed by an elevator is roughly divided into:
(a) power consumed by the hoisting motor and the hoisting unit,
(b) power consumed by the motor generator,
(c) power consumed by the control device,
(d) power consumed by illuminating lamps, electric fan, position indicating lamps, etc. in the cage, and
(e) power consumed by lamps used for indicating floor calls, position indicating lamps, cage arrival indicating lamps, etc. provided at each floor.
Among the powers consumptions described in paragraphs (a) through (e), those in paragraphs (a) and (b) are consumed as the cage moves. FIG. 1 shows variation of power consumption during the period from the start of the cage until the cage reaches a floor where it should be stopped. In FIG. 1, reference character T.sub.1 designates in acceleration period, T.sub.1 a constant speed running period, and T.sub.3 a deceleration period. Further in FIG. 1, a power consumption curve a corresponds to the case where the cage is moved upwardly at its rated load or it is moved downwardly with no load. When the cage is started, the power consumption abruptly increases. Thereafter, the difference between the rated load and the counterweight (a weight corresponding to about 50% of the rated load) is lifted, and therefore the power consumption is maintained substantially unchanged. As the cage is decelerated, regenerative power is produced although this is considerably small.
A power consumption curve b in FIG. 1 corresponds to the case where the cage is moved upwardly with no load or moved downwardly with the rated load. Similarly as for the curve a, when the cage is started, the curve has a peak. This peak, however, is smaller than the peak of the curve a. After the occurrence of the peak, the weight corresponding to 50% of the rated load is moved downwardly, and therefore potential energy is recovered, as regenerative power, by the power source. However, the amount of power actually recovered is very small because of various losses such as frictional losses and thermal losses.
Thus it may be said that, when the cage runs a certain distance, as is apparent from FIG. 1, the amount of power consumed changes depending on the cage load and the cage's maximum speed. However, in a conventional speed control system, the cage is run at maximum speed irrespective of the cage load and running distance. Therefore, the conventional speed control system is disadvantageous in that power is not economically used.
An operating method has been employed in which, when the frequency of use of an elevator is relatively small, a predetermined number of cages are operated with the maximum speed decreased, for example, to 120 m/min from 240 m/min. However, the power consumption does not always decrease, depending on cage loads and running distances, and therefore that operating method is not always effective in power reduction. Furthermore, the operating method is disadvantageous in that it takes a longer time for the cage to reach the designated floor because of the reduction in speed.